It is generally known to the person skilled in the art of rolling-element bearing technology that the support of shafts or hubs with axial and radial moment loading is usually effected by means of angular contact rolling-element bearings which, on account of the high loading, are in most cases in the form of two oppositely disposed and axially preloaded tapered roller bearings. In cases where large axial forces arise, these tapered roller bearings are configured with a large pressure angle and ensure a high stiffness of the supported shaft.
However, since in such tapered roller bearings a sliding friction between the end face of the tapered rollers and the guide face of the bearing edge is brought about due to their preload, which results in wear on the tapered rollers and the bearing edge, it was proposed in DE 198 39 481 A1 to replace the tapered roller bearings by double row angular contact ball bearings in tandem arrangement that can be loaded on one side and are disposed in an O-arrangement relative to one another. The use of such angular contact ball bearings in tandem arrangement instead of tapered roller bearings was intended to achieve a substantially smaller frictional moment because of the sliding friction no longer present between the bearing balls and the raceway shoulders, so that the wear and the temperature of the bearing are reduced and its efficiency is improved.
Nevertheless, such a replacement of tapered roller bearings by double row angular contact ball bearings in tandem arrangement has proved disadvantageous in practice, since these angular contact ball bearings in tandem arrangement require increased axial installation space, in comparison to tapered roller bearings, on account of the adjacently arranged raceways for the bearing balls and the large diameter of the bearing balls needed to achieve the required load capacity. Moreover, if such an angular contact ball bearing in tandem arrangement is to have a higher load capacity than a tapered roller bearing, costly changes to the bearing seats are necessary, disadvantageously increasing the production costs of the component concerned. Furthermore, such double row angular contact ball bearings in tandem arrangement give rise to increased manufacturing and material outlay when producing the bearings, as compared to tapered roller bearings, so that their production costs are likewise increased.
To avoid these disadvantages, it was therefore proposed in DE 10 2005 014 556, with regard to a double row angular contact rolling-element bearing consisting in a known fashion of an inner and an outer bearing ring, to configure the rolling bodies arranged between the bearing rings of each row as ball rollers with two respective lateral faces arranged parallel to one another and flattened symmetrically from a spherical basic shape, instead of bearing balls, and to arrange the two rows one beside the other with a vertical offset, in a similar manner to angular contact ball bearings in tandem arrangement with different reference circle diameters. In this case the ball rollers of the row on the larger reference circle have a larger diameter in their spherical basic shape than the ball rollers of the row on the smaller reference circle, and the two rows are retained at uniform distances from one another in the circumferential direction by a common bearing cage, with reciprocal guidance of the respective adjacent ball rollers. In addition, the ball rollers of both rows run with their running faces in two respective adjacent groove-shaped raceways in the outer and the inner bearing ring, which raceways have pressure angle axes disposed parallel to one another and are arranged contiguously to one another in such a manner that the respective adjacent ball rollers of both rows are arranged on a common axis of rotation disposed perpendicularly to the pressure angle axes. The use of ball rollers as rolling bodies is intended to distinguish such an angular contact rolling-element bearing from multi-row angular contact ball bearings primarily by a minimized axial and radial installation space, and by an equal or increased load capacity with comparable manufacturing costs.
However, it has proved in practice, in the case of the ball roller bearing in tandem arrangement proposed in DE 10 2005 014 556, that the intended synchronous running between the ball rollers arranged in a common cage pocket, resulting from the common axis of rotation of the respective adjacent ball rollers of the two rows, is lost under certain load conditions, with the consequence that friction arises between the lateral faces oriented towards one another of the respective adjacent ball rollers, as a result of different rotational speeds. If these unfavorable load conditions occur for relatively long periods or at short time intervals, this friction between the ball rollers causes a considerable temperature rise in the bearing, which can result in defective lubrication at the rolling contact and even in rupturing of the lubricating film and failure of the bearing. In addition, the direct merging of the raceways of the ball rollers, especially in the inner bearing ring, has also proved disadvantageous for the bearing kinematics, since this merging, especially in the case of a pressure angle which decreases as a result of load changes during operation of the bearing, causes the edge portions of the ball rollers of the row on the larger reference circle to slew slightly out of their raceway and therefore to have only a reduced contact area with their raceway. This in turn has the result that the pressure ellipse in the raceway resulting from the bearing load is at least partially truncated and that the ball rollers run on the edge of their raceway, resulting in damage to the running faces of the ball rollers and to their raceway.